1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of transmitting a control signal through a control channel.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 was completed in 2005 in a format of ‘corrigendum’.
Recently, standardization on the IEEE 802.16m is in progress as a new technical standard based on the IEEE 802.16e. The IEEE 802.16m, which is a newly developed technical standard, has to be designed to support the previously designed IEEE 802.16e. That is, a technology (i.e., IEEE 802.16m) of a newly designed system has to be configured to operate by effectively incorporating a conventional technology (i.e., IEEE 802.16e).
An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference. In a system using the OFDM as a modulation scheme, orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users. In the OFDMA, frequency resources (i.e., subcarriers) are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner.
In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers. In addition, a spatial multiplexing scheme using multiple antennas can be used to increase efficiency of a spatial domain. To support these various schemes, control signals must be transmitted between a user equipment (UE) and a base station (BS). Examples of the control signals include a channel quality indicator (CQI) used when the UE reports a channel condition to the BS, an acknowledgement (ACK)/not-acknowledgement (NACK) signal that is a response for data transmission, a bandwidth request signal for requesting radio resource assignment, and precoding information, antenna information, or the like used in a multiple antenna system.
Diversification of system functions results in increase in the number of types of control signals to be transmitted. When more control signals have to be transmitted with limited radio resources, an amount of radio resources to be used for user data is decreased to that extent.
Accordingly, there is a need for a method capable of effectively transmitting various control signals by using limited radio resources in an efficient manner.